Study on High Level Borehole Optimization Based on Evolving Characteristics of Mining Induced Fracture

In order to improve the gas drainage effect of high level borehole, taking No.2203 fully-mechanized top coal caving face of Zhangcun Coal Mine as the e ngineering background, combining with the mining conditions of No.3 coal seam, according to key stratum theory, the No. 3 coal seam roof fractured zones distribution range was confirmed in the range of 12. 8 ~ 36. 5 meters above the roof. By using the combined method of the thin plate theory and numerical simulation, the No. 3 coal seam roof fractured distribution and evolution characteristics during the working face mining were studied. The results showed that overburden rock stratum crack grad ually grew from the bottom up as the face advancing. At 60 meters, the dense fracture was shaped under the main key stratum. The partial main key stratum rock crack enclosed and two small compacting areas were formed between 110 meters to 170 meters, and it was gradually broaden. The coal seam roof fractured had experienced an emerge, grow and partial enclose process. Based on the findings, the disposition parameters of two group drilling field high level boreholes in No. 2203 fully-mechan ized top coal caving face was optimized. The field application showed that the amount of the optimized unit borehole gas drainage increased by 2. 39 ~ 3. 03 times, unit borehole project benefit improved by 2. 00~ 2.58 times.